MedicalResearch.com Interview with:
Ashootosh Tripathi, PhD
Postdoctoral Research Fellow
Life Sciences Institute I Sherman lab
University of Michigan
Ann Arbor, MI, USA
MedicalResearch: What is the background for this study? What are the main findings?
Dr. Tripathi: Acinetobacter baumannii is a nosocomial opportunistic and resistant pathogen that can spread epidemically among patients causing ventilator-associated pneumonia and bacteremia. The mortality rates associated with it can be as high as 60%, representing a paradigm of pathogenesis, transmission and resistance. In addition, numerous reports have shown the startling emergence of multidrug-resistant A. baumannii in hospitals as well as the identification of pan-drug-resistant strains at some locations. Among the various reasons for the antibiotic resistance of this pathogenic microbe, perhaps the most significant is mediated by its tendency to form biofilms (a highly structured extracellular polymeric matrix), which provide the microbe with the alarming ability to colonize medical devices. Interestingly, despite the well-understood role of bacterial biofilm behind aggravating antimicrobial resistance, there are currently no drugs specifically targeting biofilms in clinical trials to date. The study sought to solve this problem through the development of a biofilm inhibitor as a precision medicine, directed towards vulnerable patients, to avoid potential life-threatening infections.
A crystal-violet based high throughput in vitro screen was developed to identify inhibitors of A. baumannii biofilms against our natural products extract (NPE) library. The vast NPE library of ~42,000 extracts has been under constant development in Prof David H. Sherman laboratory at University of Michigan, Ann Arbor, for over the past decade, from a relatively underexplored marine microbiome collected from different part of world viz., Costa Rica, Panama, Papua New Guinea, etc., and is available for any research group with a robust high-throughput screening (HTS) assay (http://www.lsi.umich.edu/centers/center-for-chemical-genomics). The HTS assay that was queried against a library of 9,831 NPEs aimed to identify extracts inhibiting biofilm formation as a primary screening. Further secondary screening and activity threshold optimization revealed the extract from Streptomyces gandocaensis (collected from Costa Rica) to be of particular interest due to its ability to inhibit biofilm formation and had a limited effect on A. baumannii growth. Activity based chromatographic separation and analysis of extracts derived from S. gandocaensis resulted in the discovery of three peptidic metabolites (cahuitamycins A–C), with cahuitamycin C being the most effective biofilm inhibitor (IC50 =14.5 µM) with negligible A. baumannii growth inhibition (an important trait for ideal biofilm inhibitor). Following up on the exciting discovery, we also completely characterized the biosynthetic machinery involved in making the active molecules by S. gandocaensis, using sophisticated bioinformatics and molecular biology techniques. The knock out analysis revealed that the biosynthesis of cahuitamycin C proceeds via a convergent biosynthetic pathway, with one of the steps apparently being catalyzed by an unlinked gene encoding a 6-methylsalicylate synthase. Efforts to assess starter unit diversification through selective mutasynthesis led to production of unnatural analogues cahuitamycins D and E with increased potency (IC50=8.4 and 10.5 µM) against A. baumannii biofilm.
MedicalResearch: What should clinicians and patients take away from your report?
Dr. Tripathi: This results represent 1st instance of an effective biofilm inhibitor from marine microbial source with little to no effect on A. baumannii growth. The unique property provides cahuitamycins an edge by exerting less selective pressure on microbes to develop resistance. More importantly, traditional prophylactic antibiotic administration preceding surgery is routinely successful in reducing infection rates but it has little or no protective effects in surgical procedures involving implants or prostheses. Therefore, cahuitamycin may represent a formidable precision therapeutic option towards catheters and medical/ dental implants coated with biofilm inhibiting antimicrobial agents.
MedicalResearch: What recommendations do you have for future research as a result of this study?
Dr. Tripathi: This study clearly establishes the importance of naturally acquired molecules as a key source for novel antimicrobials. In addition, we also demonstrated preliminary structure-activity relationship indicating that a “key pharmacophore of the cahuitamycins is likely the 2-hydroxybenzoyl- oxazoline group where relatively minor modifications can result in an increase (as in case of 3–5) or decrease (as for 2) of anti-biofilm activity”. This vital moiety holds potential for further structure activity relationship studies using synthetic chemistry or through cahuitamycin biosynthetic pathway engineering. The discovery also lays down a primary foundation towards effective medicinal chemistry and synthetic formulation for development of an efficacious drug to prevent or limit biofilm formation.
MedicalResearch: Is there anything else you would like to add?
Dr. Tripathi: As WHO recognized in its recent report on global surveillance of antimicrobial resistance: “the world is heading towards a post-antibiotic era, in which common infections and minor injuries, which have been treatable for decades, can once again kill”. Our study provides an operative avenue through a largely untapped resource in marine microorganisms with impeccable potential to provide new classes of antibiotics and anti-biofilm compounds. Additionally, these results also establish “a unique opportunity for developing and discovering new antibiotics from genetically engineered strains bearing inherent flexibility in pathway initiation processes”.
Authors: Park, Sung Ryeol, Tripathi, Ashootosh, Wu, Jianfeng, Schultz, Pamela J, Yim, Isaiah, McQuade, Thomas J, Yu, Fengan, Arevang, Carl-Johan, Mensah, Abraham Y and Tamayo-Castillo, Giselle, Chuanwu Xi and David H Sherman Year: 2016
Title: Discovery of cahuitamycins as biofilm inhibitors derived from a convergent biosynthetic pathway
Journal: Nature Communications Volume: 7
Park SR, Tripathi A, et al. Discovery of cahuitamycins as biofilm inhibitors derived from a convergent biosynthetic pathway. Nature Communications 7, (2016)
Ashootosh Tripathi, PhD (2016). Discovery of Marine Microbial Cahuitamycins as Biofilm Inhibitors For Medical Devices .com